According to quantum mechanics, particles can exhibit wave-particle duality, meaning they can exhibit characteristics of both particles and waves. This duality is described by the wave function, which mathematically represents the probability distribution of a particle's properties, such as its position or momentum.
Before interacting with the external world, a particle can be described by a wave function that evolves over time according to Schrödinger's equation. This wave function behaves like a wave, exhibiting interference and diffraction phenomena. It describes the probability of finding the particle in different states or positions.
However, when a measurement or interaction occurs, the wave function collapses, and the particle's properties become definite. The act of measurement or interaction forces the particle to "choose" a specific state or position. This behavior is often referred to as wave function collapse or the observer effect.
In summary, a particle can be described as having wave-like properties before interacting with the external world, but upon interaction or measurement, its behavior becomes more particle-like, with definite properties being observed.